1976 carb issue? - loud hissing coming from main jet (1 Viewer)

[Kschep]

I’m not sure if this hissing (aka air spewing) is normal coming from the jet in the primary Venturi … I took off my air cleaner assembly to look - just sounds really loud. And maybe my ears all the sudden are just attuned to it or it’s new which I think. I was attempting to tune the carb a bit by turning the mixture screw (which I have never done before), usually I just mess with the fast idle because it’s accessible where as the mixture screw you have to take off the air cleaner assembly.
Maybe that caused something? … doubted.
Let me get some pics or a video link to youtube so y’all can hear it and see

 

[mattressking]

The loud hissing is because the engine operates on vacuum. The primary/secondary venturi uses butterflies to close off vacuum to atmospheric pressure. The more the butterfly(ies) open, the more fuel (in theory) is supposed to be pulled through each fuel circuit in the carburetor.

Clogs, incorrect jets, low vacuum, broken ICS, fuel mixture, idle screw adjustment are all items that affect running condition. Start with connecting a vacuum gauge to a pure vacuum source on intake manifold to understand how much vacuum you are seeing. Since you are at sea level, you want to be at 18-22inHg. The higher the better.

 

[Kschep]

Start with connecting a vacuum gauge to a pure vacuum source on intake manifold to understand how much vacuum you are seeing. Since you are at sea level, you want to be at 18-22inHg. The higher the better.

Awesome thx for that - will start there

 

[65swb45]

For more information on vacuum, you might want to read Section 050:

http://www.marksoffroad.net/FAQ.html

 

[peesalot]

Ah, good to hear from you. Quadrajet , they work as long as you have an unmolested one and you learn them before you adjust/tinker with it, they are actually very simple but look rather intimidating.

Thats a sucking sound, its good.